Many piping system applications in chemical and natural resource recovery industries involve corrosive, erosive, scaling or otherwise hard-to-handle fluids. One economic approach to handling these difficult fluids is to cover (or line) the interior of low cost, non-fluid-resistant pipe with a fluid-resistant liner. The composition of the resistant liner may be an inert, but brittle material, such as concrete. These brittle linings are supported by the tougher, but non-resistant pipe material, such as low carbon steel.
The supported lining material must be able to structurally withstand the severe fluid and operating environments in critical areas, such as at joints. The severe environments tend to chip, spall, crack, pit, and delaminate the lining at these critical points. These problems become especially troublesome at liner edges in certain types of joints. For example, flanged joints may need to be periodically opened for inspection, cleaning, or testing, adding further structural demands on the liner edges at these critical areas.
The primary objectives of a lined pipe joint are to: 1) allow assembly of lined pipe sections; 2) seal the joined pipe sections; 3) prevent exposure of non-resistant piping material to the harsh flowing materials; and 4) structurally withstand a variety of operating environments. If the joint is removable, joint disassembly capability is also required. The lined pipe joint device should also be light weight, rugged in construction, easy to maintain, pleasing in appearance, safe, reliable, and low in cost.
Most of the current lined pipe joints may do some of these objectives well, but other objectives may be accomplished poorly or not at all. Removable engagement (e.g., threaded joining) of liner edges at the joint may be possible for some types of liners, but is not feasible for brittle or fragile liner materials.
One conventional approach is to cap or join the liner edges to form a continuous liner across the edges. However, this requires internal access to the joint after pipe is joined. A continuous liner eliminates the liner edge problems at the joint, but joint disassembly and reassembly capability is lost or limited.
Where post-joining access is not feasible, another conventional approach is to separately seal the edges of the liner at the joint. One type of liner seal joint adds a deformable putty-like seal. The putty-like sealing material is generally unsupported. This type of sealing material may also set or harden, such as a cement slurry.
The putty-like material may also require internal access assembly. Access may be required for patching, removal of excess material, or inspection. Disassembly and reassembly capability of putty-like material sealed joint is also limited. This type of unsupported, putty-like seal may not be able to withstand elevated temperatures or thermal cycling, high pressures, and erosive or cavitating flowing fluids.
Another type of separately sealed liner joint adds a gasket or other deformable solid seal at the lining interface. A groove or retaining surface may be added to the pipe or lining material to provide support for this type of deformable seal. However, the application limits using an elastomeric material are similar to the those using a putty-like material.
A major problem with these liner seal and alternatives is the necessity of using a separate liner seal component and/or providing separate liner seal surfaces or materials. These approaches all require added liner sealing or piping costs and may adversely affect reliability and safety.
These problems are compounded in a flanged connector which is attached by butt welding to a lined pipe section. The brittle liner must be applied after welding or protected from the extreme heat during welding.
None of the current or alternative approaches known to the inventors eliminates the problem of liner edge exposure without unconventional and separate liner edge protection components or processes. Even with these added components, the reliability of current lined joints exposed to severe environments appears to be limited.